In recent years, application systems that use radio waves (for example, millimeter waves with extremely high frequencies (EHFs) of 30 GHz to 300 GHz) with strong straightness and relatively high frequencies for radio communication or radar are being actively developed. As such an application system, a phased array antenna system is known, which has antenna elements arrayed for channels and is configured to steer a radio wave beam by adjusting the phases of currents of the antenna elements, for example.
In the phased array antenna system, a large number of transmitters or receivers are used in order to increase an antenna aperture (antenna gain). However, if the number of transmitters or receivers is increased, consumed power increases. It is thus desirable that power to be consumed by amplifiers that are used in transmitters or receivers for channels be low. As a related-art document related to an increase in the gain of an amplifier, Patent Document 1 is known, for example.
As a semiconductor device (for example, a transistor) used in an amplifier that operates with a high frequency band of an EHF or higher, a compound semiconductor device, a silicon germanium (SiGe) semiconductor device, or the like is used. In recent years, due to the progress of technologies, a semiconductor device that uses a complementary metal oxide semiconductor (CMOS) is able to operate with a frequency band of an EHF or higher.